The walking type self-traveling lawn mower (hereinafter abbreviated as “lawn mower”) rotates a lawn mowing blade and drive wheels and thereby self-travels with the rotating power from a prime mover. A worker can walk and operate as holding an operation handle on a vehicle body of the lawn mower for stating-up and stopping the drive wheels, and changing direction to left or right. Such lawn mower branches the rotating power from the prime mover to the lawn mowing blade and the drive wheels. With respect to an output shaft of the prime mover, the lawn mowing blade is directly connected to said output shaft via a clutch and a brake device. The drive wheels are connected to the said output shaft via a transmission device for branching the rotating power from the output shaft.
The transmission device can be roughly classified according to the system branching the rotating power from the output shaft. Specifically, one is a transmission device of a configuration in which a shaft is connected to an auxiliary output shaft operating in conjunction with an output shaft of the prime mover (hereafter referred to as “shaft drive system”, shown in patent document 1 and patent document 2), and another is a transmission device of a configuration in which a drive pulley is attached to an output shaft of the prime mover, a driven pulley is attached to drive wheels, and a transmission belt is bridged across said drive pulley and said driven pulley (hereafter referred to as “belt drive system”, shown in patent document 3 and patent document 4). The usage of them differs depending on various situations, but generally, the large and expensive lawn mower adopts the shaft drive system, and the small and inexpensive lawn mower adopts the belt drive system.
As seen in patent document 1, in the transmission device of the shaft drive system, a reducing mechanism incorporated in the prime mover has an auxiliary output shaft, where the reduced rotating power is retrieved from the auxiliary output shaft, and the retrieved reduced rotating power is transmitted to the drive wheels by a transmission shaft coupled to the auxiliary output shaft and an universal joint. As seen in patent document 2, a configuration may also be adopted in which the auxiliary output shaft is connected to the output shaft via a simple worm gear mechanism, and then the auxiliary output shaft and the reducing mechanism arranged in the drive wheels are connected. In this case, the reducing mechanism arranged in the drive wheels may sometimes be a hydraulic stepless speed change device.
In the transmission device of the belt drive system, the drive pulley is attached to the output shaft of the prime mover, the driven pulley is attached directly to the drive wheels or to the reducing mechanism arranged in the drive wheels, and the transmission belt is wound around the drive pulley and the driven pulley so that rotating power is transmitted by the transmission belt. When winding the transmission belt around the driven pulley directly attached to the drive wheels, the radius ratio of the drive pulley and the driven pulley becomes the reduction ratio. As seen in patent document 3, the transmission device of the belt drive system has a feature in that the rotating power of the output shaft rotating horizontally can be converted to the rotating power of the drive wheels rotating vertically by twisting the transmission belt.
Patent document 1: Japanese Published Utility Model Publication No. 59-062735
Patent document 2: Japanese Published Utility Model Publication No. 63-009819
Patent document 3: Japanese Published Utility Model Publication No. 58-105824
Patent document 4: Japanese Published Utility Model Publication No. 02-031422